Arsenic
contamination is
becoming an increasingly common problem. The laboratory
detectors are expensive and incapable of permitting the
large numbers of
measurements needed in a country such as Bangladesh, where
there are over 11,000,000 wells and where there is a need to
continually
verify that the water is safe to drink. At a
conference in Dhakain December
1998, the measurement capability of the country was
estimated. A simple calculation showed that it would take 300
years for all wells to be measured.! This was clearly inadequate,
and in 2002 there were still several million untested
wells. In 2005 this most of
them have now been measured once the screening results are on the BAMWSP website.
But there should be
regular measurements of any well which is being used.
See also Feroze Ahmed's calculation of the cost.
(reproduced below) There are in general two types of
measurement equipment: Laboratory types with equipment costing
$30,000 or so, which demand that water samples be brought to the
laboratory (and for comparison split samples to several laboratories)
and field measurements that are usually based on a change in color of
some indicator.

Measurement reliability

Traditionally a country has a bureau of weights and
measured to ensure
that all merchants give proper value for money and that a kilogram of
rice
in one place is thesame as a kilogram of rice in another. There
is
regulation and frequent checking and
intercalibration. This should
be, but is not, the situation for arsenic. As a result no
one is sure whether any particlar remediation really works all the
time, and a few supposedly clean wells can in fact be laden with
arsenic with tragic results and loss of confidence. of the public in
the government and NGOs. An
interlaboratory
comparison of laboratory measurements of Arsenic was organized at the
International Atomic Energy Agency in 2001 and is
available in draft form. Available also is a
comment there on. The results were not encouraging. The
expectation is that calibration of the field kits
might well be worse. In this webmaster's view, ensuring the
reliability of the measurements should be a high priority particularly
in Bangladesh. Those trying to bring pure water to the peopleand
those engaged in epidemiological analyses should not have to worry
about the reliability of these measurements in addition to their other
tasks. However recent (May 2005) unpublished
comparisons suggest that there is great improvement. Only
one out of 11 tested laboratories failed to measure consistently,
although 4 of the 11 were inaccurate. However, although a
laboratory reading systematially 30% low must correct its practices,
this error is not imporatnt inn any decision to
date.

Sodium chloride, iron, sulfate, and acidity can potentially interfere
with arsenic measurements in water. However, in general, EPA found that
the test kits and portable chemical sensors were not affected by the
presence of sodium chloride, iron, sulfate, or acidity, and that
measurements of arsenic were similar in samples that contained these
potential interfering chemicals vs. samples that did not. EPA did find
that high iron and/or hydrogen sulfide concentrations biased arsenic
measurements by the PDV 6000 analyzer. Arsenic results in samples with
high concentrations of iron and/or hydrogen sulfide were biased high.

Standard
Methods.

The following is from standard
measurement methods for waste
water "3500-As
Arsenic (20th Edition)" in 1997. Standard measurements is
now available on line/

Methods are available to identify
and determine total arsenic,
arsenite, and arsenate. Unpolluted fresh water normally does not
contain organic arsenic compounds, but may contain inorganic arsenic
compounds in the form of arsenate and arsenite. The electrothermal
atomic absorption spectrometric method (3113) is the method of choice
in the absence of overwhelming interferences. The hydride
generation-atomic absorption method (3114) is preferred when
interferences are present that cannot be overcome by standard
electrothermal techniques (e.g., matrix modifiers, background
correction). The silver diethyldithiocarbamate method (3500-As B), in
which arsine is generated by reaction with sodium borohydride in acidic
solution, is applicable to the determination of total inorganic arsenic
when interferences are absent and when the sample contains no
methylarsenic compounds. This method also provides the advantage of
being able to identify and quantify arsenate and arsenite separately by
generating arsine at different pHs. The inductively coupled
plasma (ICP) method (3120) is useful
at higher concentrations (greater than 50 µg/L) while the
ICP/mass
spectrometric method (3125) is applicable at lower concentrations if
chloride does not interfere. When measuring arsenic species, document
that speciation does not change over time. No universal preservative
for speciation measurements has been identified.

An excellent up to date review of the methods was presented at the
March 2006 American Chemical Society meeting by Dr Hussam of George
Mason University, USA in March 2006. When available ythe details
will be posted on this site

Field Kits:
1) Peters Engineering PeCo 75 and As 75 based
on arsine generation
(same thing, one with electronic color measurer,
one visual)
2) Envitop
Ltd. As-Top Water arsenic test kit; based on arsine generation
3) Industrial
Test Systems, Inc., QuickT test kit arsenic analysis systems; based
on arsine generation.
4) NANO-BAND
EXPLORER Portable Water Analyzer; using stripping anodic
voltammetry.
The above four were tested in 2002 by the USEPA
as part of their Environmental Technology Verification Program

The Merck kit is the most
widely used. Tests were reported in the arsenic conference
at DCH Dhaka in May 2000 and this was the only kit
widely recommended. But at that time it could only measure
arsenic
content above 100 microgram per liter (100 ppb) and even then is
considered to be unreliable by many
investigators. In January 2002 some investigators trust it to 50
microgram per liter (100 ppb) but this does not seem to have been
proven. Arsenic Solutions are also
working with the Finns to market their "Merck-type" field test kit,
which seems
to be improving all the time. The new version is slightly more
expensive
than the Merck kit and is claimed tol provide good results down to
concentrations
of arsenic in the water of 10 ppb, even when sulfide is present, as is
common in Bangladesh. Arsenic Solutions also have a soil kit which Matt
Simmons thinks is unique8)
UNICEF field kit No data available on this9) Hach Field kit
Some workers in the field claim that the Hach field kit is more
sensitive and more reliable than the Merck kit. The
Columbia
University scientists, in particular, have used it but recommend
allowing 40 minutes for the measurements instead of the 20 minutes
recommended by Hach. This, Columbia University
scientists claim,
improves the
reliability. However the Hach kit is
generally less used because some field workers find it to be
fragile.
10) CLEAN
INDIA arsenic field kit. This is made by CLEAN INDIA of New
Delhi and is now being tested in the field in Bangaldesh and West
Bengal.
11) Monitoring Technologies International, Pty.
Ltd.PDV 6000 Portable Analyzer (August
2003) Verification
Report Verification
Statement12)
Equipment exists for X `ray fluorescence. It is unclear whether
this will work well for 10 ppb arsenic in the presence of 10 ppm of
other chemicalsRoentec Ag
BerlinPrinciplesTypical TraceArticle

This recent system involves
the generation of light by modified E. coli in a solution.
The amount of light emitted allows quantitative measurements of
the
heavy metal content. It measures either TOTAL arsenic or arsenic
III content to about 1 ppb. Matt Simmons
believes
it can be cheap and made on the Indian Subcontinent.

A
combination chemical
and
electronic device has been devised by Dr. Walter Kosmos of the
University of Graz inAustriaand called "The Arsenator".
This comes in
two forms. Alaboratory instrument capable of accuate
(3%)
measurements down to1 microgramper litre (1 ppb) and a field
instrument
capable of 10%measurementsdownto 5 microgramper litre (5
ppb).
This deviceseems to be most promising and has the potential to
meet
the need. However,
at the 3rd International Arsenic Conference in Dhaka (May 2000) it was
reported that the ARSENATOR is hard to use. Batteries are
unconventional
(for Bangladesh) and do not last. Dust gets into the
instrument. It is fervently hoped that these difficulties can be
overcome. The capital cost of $1500 is high but it should
be justifiable - if many measurements are taken.
Since one measurement takes 15 minutes, this could be done and is
"only" a matter of organization. The
Arsenator was independently
field tested in Myanmar by Dr Peter Swash, Imperial College, London and
a team from the local UNICEF field office. It seems that Wagtech International is now
an arsenator sales representative. (Nick Price, Sales & Marketing
Director, Wagtech International, United KingdomTEl:: +44 (0) 1635 872929; FAX: +44 (0)
1635 862898; mobile/cell +44 (0) 7710 102182

(3) Direct reading Equipment exists for X `ray fluorescence. It is unclear whether this will work well for 10 ppbarsenic in the presence of 10 ppm of other chemicals

Everyone who has looked for
microbiological contamination in water that has not been stored
carefully has found gross
contamination - water containers act as incubators in the house,
especially when they are uncovered or do not have taps. After 12 hours,
fecal coliforms can be more than 10,000/100ml, or even 'TNTC' (too
numerous to count). Dugwells if they are uncovered can have
coliform bacteria also. The primary way of avoiding such
bacteria is to insist on santiary conditions: Covered dugwells
to keep out animals and pets and fecal matter. But it is
therefore very important to measure
coliform bacterial
contamination. In principle this is easier than
measuring low levels of arsenic and should be cheaper although it seems
to cost about the same as testing for arsenic with a field kit.
An Indian made kit (
by Clean India )
cleanindia@sdalt.ernet.in.is available
for measuring coliform bacteria and other contaminants (but not arsenic) at a cost of about
$1 per measurement. This has been used for the last few years by Dhaka
Community Hospital and has proven easy to use. This
kit maybe accessed directly at http://www.cleanindia.org/jaltarakit.htm or by e -mail to:temf@sdalt.ernet.in.

Laboratory measurement procedures:

Dr.
Purnendu Dasgupta from Texas Tech University. Dr. Dasguptais
developing, researching and testing a field-deployable instrument for
the measurement and speciationof arsenic in potable water.
To see a copy of Dr. Dasgupta's paper on his arsenic
detection device,
click here.

The arsenic content of water of tubewells within short distances
varies widely in many palces. This is probably due to variation in the
depth
of tubewellsand geoenvironmental conditions of the strata of aquifers
from
which the tube wells abstract water. As a result, the levels of
contamination
in an area cannot be accurately predicted by testing of water of sample
tubewells.Screening of all tubewells in the country is needed to
identify the contaminated tubewell. Government of Bangladesh has
decided to test arsenic content of water
produced by all tubewells to identify the safe and unsafe tubewells.
Bangladesh
Arsenic Mitigation Water Supply Project and UNICEF have so far
completed
screening of all tubewells of 41 Upazillas and 5 Upazilas
respectively.The
estimated cost of field test kit only for the screening of estimated
7.5 million
tube wells in the country is given below:

The number of contaminated tubewells estimated on the basis of
sample survey conducted by BGS and DPHE (2001) is 1.875 million which
is
25% of
the total estimated 7.5 million tubewells in Bangladesh. The present
cost
of this 1.875 million tubewells is Taka 8.44 billion. The significant
deviations
in intensity of contaminated tube wells by total screening from
BGS/DPHE
values justify the national screening program.

Monitoring
of "safe" wells after screening:

The estimated 5.625 million manually operated deep and shallow
tubewells still supplying water with arsenic below national
standard to
83 million people in the country are vulnerable to arsenic
contamination
in future. No mathematical model can correctly predict the
possible or
probable
time of contamination of these tubewells. In this situation, monitoring
is
the only way to know whether the tubewell is contaminated or not. The
estimated
cost of field kits for monitoring of the safe tubewells once per
year using a "field kit". is
given below. Laboratory measurements, which would be necessary
for low levels, would be more expensive.

Since it is estimated that 87% tubewells are likely to be privately
owned, testing
of water for arsenic should be the responsibility of the owner. The
testing of tube well water once in a year could be made mandatory.
Most experts recommend that a good test facility should be
available locally, preferably at the lowest
level of the Local Government body. However this is not yet
the case (2006).

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